Abstract
Osteoarticular tuberculosis of the knee is an uncommon disease presentation, especially in children under 1 year old. Diagnosis based on classic methods (such as culture and anatomopathological examination) is a challenge due to the paucibacillary characteristic of the infection. Risk factors include contact with individuals with bacilliferous tuberculosis, living in a region with high disease prevalence, and pediatric age group. We describe a case of chronic monoarthritis caused by Mycobacterium tuberculosis and intermittent inflammatory manifestations in a 10-month-old male patient with no extra-articular symptoms and no history of contact with bacilliferous tuberculosis. The culture was negative, and the anatomopathological examination was inconclusive for the etiologic agent. The detection of traces of M. tuberculosis DNA by a rapid molecular test (GeneXpert) based on the polymerase chain reaction technique established the diagnosis. The treatment consisted of antituberculosis drugs and led to complete resolution of the clinical-radiographic picture. This case emphasizes the importance of considering tuberculosis in the initial differential etiologic diagnoses of arthritis and, therefore, the need for an early, specific investigation, even when the clinical suspicion is not high.